scholarly journals Evaluation of Surface Melt on the Greenland Ice Sheet using SMAP L-Band Microwave Radiometry

2021 ◽  
pp. 1-1
Author(s):  
Mohammad Mousavi ◽  
Andreas Colliander ◽  
Julie Z. Miller ◽  
Dara Entekhabi ◽  
J. Johnson ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Microwave Radiometry ◽  
L Band ◽  
Surface Melt

scholarly journals An empirical algorithm to map perennial firn aquifers, ice slabs, and perched firn aquifers within the Greenland Ice Sheet using satellite L-band microwave radiometry

2021 ◽  
Author(s):  
Julie Z. Miller ◽  
Riley Culberg ◽  
David G. Long ◽  
Christopher A. Shuman ◽  
Dustin M. Schroeder ◽  
...  
Keyword(s):  
Spatial Scales ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Melting ◽  
Snow Accumulation ◽  
Rapid Expansion ◽  
Microwave Radiometry ◽  
Subsurface Water ◽  
L Band ◽  
Water Saturated

Abstract. Perennial firn aquifers are subsurface meltwater reservoirs formed from a water-saturated firn layer. They have been observed within the percolation facies of glaciated regions experiencing intense seasonal surface melting and high snow accumulation. Widespread perennial firn aquifers have been identified within the Greenland Ice Sheet (GrIS) via field expeditions, airborne ice-penetrating radar surveys, and satellite microwave sensors. In contrast, ice slabs are nearly-continuous ice layers that form on spatial scales of kilometers as a result of surface and subsurface water-saturated snow and firn layers sequentially refreezing following multiple melting seasons. They have been observed within the percolation facies of glaciated regions experiencing intense seasonal surface melting, but in areas where snow accumulation is at least ~25 % lower as compared to perennial firn aquifer areas. Widespread ice slabs have recently been identified within the GrIS via field expeditions and airborne ice-penetrating radar surveys, specifically in areas where perennial firn aquifers typically do not form. However, ice slabs have yet to be inferred from space. Together, these two ice sheet features represent distinct, but related, sub-facies within the broader percolation facies of the GrIS that can be defined primarily by differences in snow accumulation, which influences the englacial hydrology and thermal characteristics of firn layers at depth. Here, for the first time, we use enhanced-resolution vertically-polarized L-band brightness temperature (TBV) imagery (2015–2019) generated using observations collected over the GrIS by NASA’s Soil Moisture Active Passive (SMAP) satellite to map both perennial firn aquifer and ice slab areas as a continuous system over the percolation facies. We also map “perched” firn aquifer areas, which we define as areas where shallow water-saturated firn layers transiently form on top of buried ice slabs, or other semi-impermeable layers within the snow and firn. An empirical algorithm previously developed to map the extent of Greenland’s perennial firn aquifers via fitting exponentially decreasing temporal L-band signatures to a set of sigmoidal curves is recalibrated to also map the extent of ice slab and perched firn aquifer areas using airborne ice-penetrating radar surveys collected by NASA’s Operation Ice Bridge (OIB) campaigns (2010–2017). Our SMAP-derived maps show that between 2015 and 2019, perennial firn aquifer areas extended over ~64,000 km2, ice slab areas extended over ~76,000 km2, and perched firn aquifer areas extended over ~37,000 km2. Combined together, these three sub-facies are the equivalent of ~24 % of the percolation facies of the GrIS. As Greenland’s climate continues to warm, and seasonal surface melting increases in extent, intensity, and duration, quantifying the possible rapid expansion of each of these sub-facies using satellite L-band microwave radiometry has significant implications for understanding ice sheet-wide variability in englacial firn hydrology resulting in meltwater-induced hydrofracturing and accelerated ice flow as well as high-elevation run-off that can impact the mass balance and stability of the GrIS.

scholarly journals An empirical algorithm to map perennial firn aquifers and ice slabs within the Greenland Ice Sheet using satellite L-band microwave radiometry

2022 ◽  
Vol 16 (1) ◽  
pp. 103-125
Author(s):  
Julie Z. Miller ◽  
Riley Culberg ◽  
David G. Long ◽  
Christopher A. Shuman ◽  
Dustin M. Schroeder ◽  
...  
Keyword(s):  
Spatial Scales ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Melting ◽  
Snow Accumulation ◽  
Rapid Expansion ◽  
Microwave Radiometry ◽  
Subsurface Water ◽  
L Band ◽  
Water Saturated

Abstract. Perennial firn aquifers are subsurface meltwater reservoirs consisting of a meters-thick water-saturated firn layer that can form on spatial scales as large as tens of kilometers. They have been observed within the percolation facies of glaciated regions experiencing intense seasonal surface melting and high snow accumulation. Widespread perennial firn aquifers have been identified within the Greenland Ice Sheet (GrIS) via field expeditions, airborne ice-penetrating radar surveys, and satellite microwave sensors. In contrast, ice slabs are nearly continuous ice layers that can also form on spatial scales as large as tens of kilometers as a result of surface and subsurface water-saturated snow and firn layers sequentially refreezing following multiple melting seasons. They have been observed within the percolation facies of glaciated regions experiencing intense seasonal surface melting but in areas where snow accumulation is at least 25 % lower as compared to perennial firn aquifer areas. Widespread ice slabs have recently been identified within the GrIS via field expeditions and airborne ice-penetrating radar surveys, specifically in areas where perennial firn aquifers typically do not form. However, ice slabs have yet to be identified from space. Together, these two ice sheet features represent distinct, but related, sub-facies within the broader percolation facies of the GrIS that can be defined primarily by differences in snow accumulation, which influences the englacial hydrology and thermal characteristics of firn layers at depth. Here, for the first time, we use enhanced-resolution vertically polarized L-band brightness temperature (TVB) imagery (2015–2019) generated using observations collected over the GrIS by NASA's Soil Moisture Active Passive (SMAP) satellite to map perennial firn aquifer and ice slab areas together as a continuous englacial hydrological system. We use an empirical algorithm previously developed to map the extent of Greenland's perennial firn aquifers via fitting exponentially decreasing temporal L-band signatures to a set of sigmoidal curves. This algorithm is recalibrated to also map the extent of ice slab areas using airborne ice-penetrating radar surveys collected by NASA's Operation IceBridge (OIB) campaigns (2010–2017). Our SMAP-derived maps show that between 2015 and 2019, perennial firn aquifer areas extended over 64 000 km2, and ice slab areas extended over 76 000 km2. Combined together, these sub-facies are the equivalent of 24 % of the percolation facies of the GrIS. As Greenland's climate continues to warm, seasonal surface melting will increase in extent, intensity, and duration. Quantifying the possible rapid expansion of these sub-facies using satellite L-band microwave radiometry has significant implications for understanding ice-sheet-wide variability in englacial hydrology that may drive meltwater-induced hydrofracturing and accelerated ice flow as well as high-elevation meltwater runoff that can impact the mass balance and stability of the GrIS.

scholarly journals Quantifying Surface Melt and Liquid Water on the Greenland Ice Sheet using L-band Radiometry

2021 ◽  
Vol 256 ◽  
pp. 112341
Author(s):  
Derek Houtz ◽  
Christian Mätzler ◽  
Reza Naderpour ◽  
Mike Schwank ◽  
Konrad Steffen
Keyword(s):  
Liquid Water ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
L Band ◽  
Surface Melt

Greenland land-terminating glaciers velocity trends during the last two decades

2021 ◽  
Author(s):  
Paul Halas ◽  
Jeremie Mouginot ◽  
Basile de Fleurian ◽  
Petra Langebroek
Keyword(s):  
Water Pressure ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Melting ◽  
Limited Area ◽  
Ice Dynamics ◽  
Basal Sliding ◽  
Surface Melt ◽  
Ice Sheet Dynamics ◽  
The Impact

<div> <p>Ice losses from the Greenland Ice Sheet have been increasing in the last two decades, leading to a larger contribution to the global sea level rise. Roughly 40% of the contribution comes from ice-sheet dynamics, mainly regulated by basal sliding. The sliding component of glaciers has been observed to be strongly related to surface melting, as water can eventually reach the bed and impact the subglacial water pressure, affecting the basal sliding.  </p> </div><div> <p>The link between ice velocities and surface melt on multi-annual time scale is still not totally understood even though it is of major importance with expected increasing surface melting. Several studies showed some correlation between an increase in surface melt and a slowdown in velocities, but there is no consensus on those trends. Moreover those investigations only presented results in a limited area over Southwest Greenland.  </p> </div><div> <p>Here we present the ice motion over many land-terminating glaciers on the Greenland Ice Sheet for the period 2000 - 2020. This type of glacier is ideal for studying processes at the interface between the bed and the ice since they are exempted from interactions with the sea while still being relevant for all glaciers since they share the same basal friction laws. The velocity data was obtained using optical Landsat 7 & 8 imagery and feature-tracking algorithm. We attached importance keeping the starting date of our image pairs similar, and avoided stacking pairs starting before and after melt seasons, resulting in multiple velocity products for each year.  </p> </div><div> <p>Our results show similar velocity trends for previously studied areas with a slowdown until 2012 followed by an acceleration. This trend however does not seem to be observed on the whole ice sheet and is probably specific to this region’s climate forcing. </p> </div><div> <p>Moreover comparison between ice velocities from different parts of Greenland allows us to observe the impact of different climatic trends on ice dynamics.</p> </div>

scholarly journals Greenland ice sheet melt area from MODIS (2000–2014)

2020 ◽  
pp. 57-60
Author(s):  
Robert S. Fausto ◽  
Dirk Van As ◽  
Jens A. Antoft ◽  
Jason E. Box ◽  
William Colgan
Keyword(s):  
Global Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Internet Portal ◽  
Sheet Surface ◽  
Glacier Ice ◽  
Key Driver ◽  
Surface Melt ◽  
Global Sea Level ◽  
Terra Satellite

The Greenland ice sheet is an excellent observatory for global climate change. Meltwater from the 1.8 million km2 large ice sheet infl uences oceanic temperature and salinity, nutrient fl uxes and global sea level (IPCC 2013). Surface refl ectivity is a key driver of surface melt rates (Box et al. 2012). Mapping of diff erent ice-sheet surface types provides a clear indicator of where changes in ice-sheet surface refl ectivity are most prominent. Here, we present an updated version of a surface classifi cation algorithm that utilises NASA’s Moderateresolution Imaging Spectroradiometer (MODIS) sensor on the Terra satellite to systematically monitor ice-sheet surface melt (Fausto et al. 2007). Our aim is to determine the areal extent of three surface types over the 2000–2014 period: glacier ice, melting snow (including percolation areas) and dry snow (Cuff ey & Paterson 2010). Monthly 1 km2 resolution surface-type grids can be downloaded via the CryoClim internet portal (www.cryoclim.net). In this report, we briefl y describe the updated classifi cation algorithm, validation of surface types and inter-annual variability in surface types.

scholarly journals Ice sheet mass loss caused by dust and black carbon accumulation

2015 ◽  
Vol 9 (2) ◽  
pp. 2563-2596
Author(s):  
T. Goelles ◽  
C. E. Bøggild ◽  
R. Greve
Keyword(s):  
Mass Loss ◽  
Black Carbon ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Carbon Accumulation ◽  
Model Framework ◽  
Ice Dynamics ◽  
Ablation Area ◽  
Ice Surface ◽  
Surface Melt

Abstract. Albedo is the dominating factor governing surface melt variability in the ablation area of ice sheets and glaciers. Aerosols such as mineral dust and black carbon (soot) accumulate on the ice surface and cause a darker surface and therefore a lower albedo. The dominant source of these aerosols in the ablation area is melt-out of englacial material which has been transported via ice flow. The darkening effect on the ice surface is currently not included in sea level projections, and the effect is unknown. We present a model framework which includes ice dynamics, aerosol transport, aerosol accumulation and the darkening effect on ice albedo and its consequences for surface melt. The model is applied to a simplified geometry resembling the conditions of the Greenland ice sheet, and it is forced by several temperature scenarios to quantify the darkening effect of aerosols on future mass loss. The effect of aerosols depends non-linearly on the temperature rise due to the feedback between aerosol accumulation and surface melt. The effect of aerosols in the year 3000 is up to 12% of additional ice sheet volume loss in the warmest scenario.

scholarly journals Firn temperature and meltwater refreezing in the lower accumulation area of the Greenland ice sheet, Pâkitsoq, West Greenland

1993 ◽  
Vol 159 ◽  
pp. 109-114
Author(s):  
R.J Braithwaite
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
International Project ◽  
Sea Level Changes ◽  
West Greenland ◽  
Degree Day ◽  
Air Temperatures ◽  
Surface Melt ◽  
High Degree

Firn temperatures and meltwater refreezing are studied in the lower accumulation area of the Greenland ice sheet as part of an international project on sea level changes. In the study area, 1440–1620 m a.s.l., meltwater penetrates several metres into the firn and refreezes, warming the firn by 5–7°C compared with annual air temperatures. This firn warming is closely related to surface melt which can be estimated by several methods. A relatively high degree-day factor is needed to account for the melt rates found.

scholarly journals Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers

2012 ◽  
Vol 6 (1) ◽  
pp. 593-634 ◽  
Author(s):  
J. E. Box ◽  
X. Fettweis ◽  
J. C. Stroeve ◽  
M. Tedesco ◽  
D. K. Hall ◽  
...  
Keyword(s):  
Solar Energy ◽  
Climate Model ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Dominant Factor ◽  
Water Runoff ◽  
Albedo Feedback ◽  
Ablation Area ◽  
Regional Climate Model Output ◽  
Surface Melt

Abstract. Greenland ice sheet mass loss has accelerated in the past decade responding to combined glacier discharge and surface melt water runoff increases. During summer, absorbed solar energy, modulated at the surface primarily by albedo, is the dominant factor governing surface melt variability in the ablation area. Using satellite observations of albedo and melt extent with calibrated regional climate model output, we determine the spatial dependence and quantitative impact of the ice sheet albedo feedback in twelve summer periods beginning in 2000. We find that while the albedo feedback is negative over 70 % of the ice sheet, concentrated in the accumulation area above 1500 m, positive feedback prevailing over the ablation area accounts for more than half of the overall increase in melting. Over the ablation area, year 2010 and 2011 absorbed solar energy was more than twice as large as in years 2000–2004. Anomalous anticyclonic circulation, associated with a persistent summer North Atlantic Oscillation extreme since 2007 enabled three amplifying mechanisms to maximize the albedo feedback: (1) increased warm (south) air advection along the western ice sheet increased surface sensible heating that in turn enhanced snow grain metamorphic rates, further reducing albedo; (2) increased surface downward solar irradiance, leading to more surface heating and further albedo reduction; and (3) reduced snowfall rates sustained low albedo, maximizing surface solar heating, progressively lowering albedo over multiple years. The summer net radiation for the high elevation accumulation area approached positive values during this period.

scholarly journals Passive microwave-derived spatial and temporal variations of summer melt on the Greenland ice sheet

1993 ◽  
Vol 17 ◽  
pp. 233-238 ◽  
Author(s):  
Thomas L. Mote ◽  
Mark R. Anderson ◽  
Karl C. Kuivinen ◽  
Clinton M. Rowe
Keyword(s):  
Time Series ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Late Summer ◽  
Temporal Variations ◽  
Early Summer ◽  
Passive Microwave ◽  
Brightness Temperatures ◽  
Surface Melt ◽  
Major Surface

Passive microwave-brightness temperatures over the Greenland ice sheet are examined during the melt season in order to develop a technique for determining surface-melt occurrences. Time series of Special Sensor Microwave/ Imager (SSM/I) data are examined for three locations on the ice sheet, two of which are known to experience melt. These two sites demonstrate a rapid increase in brightness temperatures in late spring to early summer, a prolonged period of elevated brightness temperatures during the summer, and a rapid decrease in brightness temperatures during late summer. This increase in brightness temperatures is associated with surface snow melting. An objective technique is developed to extract melt occurrences from the brightness-temperature time series. Of the two sites with summer melt, the site at the lower elevation had a longer period between the initial and final melt days and had more total days classified as melt during 1988 and 1989. The technique is then applied to the entire Greenland ice sheet for the first major surface-melt event of 1989. The melt-zone signal is mapped from late May to early June to demonstrate the advance and subsequent retreat of one “melt wave”. The use of such a technique to determine melt duration and extent for multiple years may provide an indication of climate change.

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